[Patent document 1] JP-A-2008-122149
For instance, Patent document 1 recites a conventionally known apparatus to detect whether a steering wheel of a vehicle is held or gripped with both hands of a driver, based on a signal inputted from a sensor in-bedded in the steering wheel. In the apparatus recited in Patent document 1, when it is detected that the steering wheel is held by one hand of the driver, a travel state of the vehicle is determined whether to be within-stipulated or without-stipulated. The without-stipulated travel state is defined as a travel state where the driving manipulation with the steering wheel gripped by only one hand is inevitable. The within-stipulated travel state is other than the without-stipulated travel state. When the determined travel state is within-stipulated warning is outputted so as to warn the driver of driving the vehicle more safely.
In Patent document 1, the without-stipulated travel state includes the following: when the vehicle is moved backward; when the vehicle is rotated; when an in-vehicle instrument necessary for driving the vehicle (for example, a shift lever, or a blinker, a head lamp switch) is manipulated; and when the vehicle is in traffic congestion.
The state, where a driver performs a driving manipulation while holding or gripping the steering wheel with a single hand, may includes a state where the driver puts the hand, which is not gripping the steering wheel, on an armrest or window frame in the vehicle while performing the driving manipulation. In such a case, while relaxing moderately, the driver of the vehicle still concentrates on the driving manipulation, thereby usually enabling the vehicle to be driven safely in many cases.
Although the vehicle is driven still safely even with the steering wheel held with a single hand, such a state is defined as not according with the without-stipulated travel state in Patent document 1 thereby outputting a warning to the driver. That is, the warning is outputted to the driver concentrating on driving manipulation. The sense of incongruity is thus given to the driver; by contrast, the warning may lower the concentration of the driver on the driving manipulation.
That is, in Patent document 1, there is a disadvantage or problem that a warning is not suitably outputted to the driver in consideration of various states of the driver taking place at the time when the steering wheel of the vehicle is held with a single hand.